In various portable devices, such as cellular telephones, the need to provide stable DC operating conditions can be important. To obtain such stable DC operating conditions, a regulated voltage is often used. Such regulated voltages are useful to provide stable low noise amplifiers, variable gain amplifiers and power amplifiers.
Unfortunately, certain portable devices, such as cellular phones and PDAs, may use a battery as it sole power source. Because batteries do not provide constant voltages under varying conditions, electronic circuits that rely on stable DC voltages may perform poorly.
In order to compensate for this shortcoming, voltage regulating circuits, such as Low-DropOut regulators (LDOs) are used in conjunction with batteries. However, as the number of functions of portable devices (e.g., multimedia and camera) increase, the number of LDOs may also increase.
Unfortunately, the number of the LDOs available to a portable device may be limited due to area constraints. Thus, it is desirable to develop bias circuitry for amplifiers that can provide constant bias conditions over large battery voltage variations.